With development of hardware and software technology of mobile terminals and wireless communication technology, direct terminal-to-terminal communication technology (Device to Device, i.e., D2D, which is a direct terminal-to-terminal communication technology introduced in the 3GPP Rel-12, allowing users to transmit data not via cellular network infrastructure) gradually becomes an important technology. The D2D technology mainly includes D2D discovery (i.e., discovery phase) and D2D communication (i.e., communication phase). The D2D discovery and the D2D communication are independent services. The D2D communication allows two user equipment to directly send and transmit data via a specific channel (sidelink channel), without transmitting via a base station. The D2D communication can be used for commercial scenarios and public security scenarios, and is a technology highly valued by many states and multinational companies currently, and is also a technology which may have a significant impact on terminal products in future.
The D2D communication includes a scenario with network coverage and a scenario without network coverage. Under the scenario with network coverage, if spectrum resources of a macro network side are used in the D2D communication, the resources used by the D2D communication should be managed and controlled on the network side. In prior art, two modes of allocating time-frequency resource used in the D2D communication are already provided for the scenario with network coverage. One is the D2D communication based on direct scheduling (hereinafter referred to as mode A). Specifically, a UE (User Equipment) is in a connected state, and a base station instructs, by signaling, a transmitter when and in which resource block the UE performs data transmission, such a resource allocation being based on each UE. The other is the D2D communication based on shared resources (hereinafter referred to as mode B). The primary concept thereof is that UEs in one cell shares a time-frequency resource pool broadcasted by a base station and performs the D2D communication. The foregoing two allocation modes have their own advantages and disadvantages, respectively, and both are actually necessary solutions.
Currently, when the 3GPP discusses the D2D communication solution based on direct scheduling, there is a following problem: when the macro network coverage where the UE is located is poor, the UE which is in a connected state and communicates under the mode A may not obtain resources of the mode A from a base station for a certain period. If the UE still need to use the resources of the mode A during this period, the D2D communication may not be performed, resulting in interruption of the D2D communication.
Therefore, how to effectively reduce likelihood of the interruption of the D2D communication and guarantee continuity of D2D communication service is a problem to be solved.